Method of producing a hard metal alloy



APR 14 a:

um A g. 22,1939

Paul Schwarzkopf, mat, Austria, assignor to American-Cutting Alloys,Inc., New York, N. Y., a corporation of Delaware ,No Drawing.Application September 16, 1987.

, aims-33;

Serial No. 164,186. In Germany May 16, 1929 1 7 Claims. (Cl. 75-137)This invention refers to a hard metal tool alloy and method of producingthe same.

This inventioniorms a continuation in part of my copending applicationSer. No. 727,781,

5. filed May 26, 1934, and of my copending application Ser. No. 743,717,filed September 12, 1934 and issued into Patent No. 2,122,157, whichwere in turn copending with my application Ser. No. 656,103, filedFebruary 10, 1933 and issued into Patent No. 1,959,979, and myapplication Ser. No.

;, It is an object of the invention to increase the 625,042, flled July27, 1932 and issued into Patent No. 2,091,017, which were in turncopending with myapplication Ser. No. 452,132, filed May 13,

hardness of suchhard metal tool alloys without impairing theirtoughness. I

It is another object of the invention to increase the resistance of suchhard metal tool alloys i-against mechanical wear and chemical effectssuch as of the oxygen of the surrounding air, or moisture, or 'a coolingliquid such as water.

It is a further object of the invention to increase tlie hardness ofthe" alloy without impairing its toughness and the size of hardparticles contained therein.

It is another object of the invention to adjust the heat conductivity ofthe hard metal tool alloy without impairing its hardness or resistanceagainst oxidation.

It is still another object of the-invention to increase the speed atwhich hard "alloys of this mod can be used for cutting, drilling,milling, and other machining purposes. I This and other objects of theinvention will be more clearly understood when the specificationproceeds.

Hard metal tool alloys of the type referred to have been made oftungsten carbide and aumli'ary metal taken substantially from theirongroup, in amounts from about 3% to 20%. The tungsten carbide hasbeen finely powdered and mixed with the auxiliary metal, and the mixtureheated to sintering temperature. Such hard metal tool 221-,

.- loys could be utilized for machining cast iron but do not proveeificient in high speed machining steel and other compositions of metal.

In contradistinction hereto the invention proceeds from fundamentallynew considerations. It no longer uses one carbide alone, viz. tungstencarbide, and cements it by auxiliary metal in the heat.

The present invention particularly refers to a method of producing ahard metal composition, comprising a'consolidated product consistingsuband 10% Co the material is brittle.

stantially of about 3% to 22% auxiliary metal essentially of the irongroup, and at least two carbides of tungsten, molybdenum (i. e. anelement of the sixth group of the periodical systern), boron (i. e. anelement of the third group of the periodical system), silicon, titanium,zirconium (he. an element of the fourth group of the periodical system)and vanadium (i. e. an element of the fifth group of the periodicalsystem) and in general of at least two hard'carbides of diflerentelements selected from the third through sixth groups of the periodicalsystem. The invention comprises the steps of comminutins. Preferably asfinely as possible, at least two hard carbides selected from the thirdthrough sixth groups of the periodical system, admixing the selectedcarbides in substantial amounts, in-

eluding a minimum or 1% of a selected carbide, ,with auxiliary metalessentially of the iron group in amounts of about 3% to 22%, shaping andpreferably pressing the mixture and finally alloying it bysintering itinto' a hard and tough body and until mixed crystals of selectedcarbides are formed therein in substantial amounts.

A mixed crystal is a homogeneous solid solution of two (or more)substances capable of dissolving one in the'other. Experiments haveshown and science has given the rule that the hardness of the mixedcrystals is a function of the proportion in which the carbides arepresent in the mixed crystal, and that this function possesses a mammum.It is particularly advantageous to choose for use in the presentinvention crystals which lie in, or close to this range of mammumhardness. Let me take first experiments made for instance with MOsC, W2Cand 00, let me increase the amount of Meat. while decreasing the amountof W2C, adding always 10% Co; then (1) -W2C and 0% M020 and 10% Co givesa Rockwell hardness of 55; (2) 81% W2C. and 9% MOzC and. 10% Co gives aRockwell hardness of 62; (3) 72% W20 and 18% M020 and 10% Co gives aRockwell hardness of 57.5: while (4) with 63% W2C and 27% M020 By thesefew tests it is possible to ascertain the hardest mixed crystal of therespective series.

Most favorable results have been obtained with mixed crystals of thesystem Moira-WC. The

maximum hardness is obtained with an alloy containing about 63% oftunssten-monooarbide (WC), 27% ofmolybdenum carbide and 10% of cobalt;this alloy has a hardness of 69 Rockwell (diamond load= kg).Satisfactory results are obtained with alloys within the compositionrange: 50% to 70% tungsten-monocarbide (WC), 40% to 20% molybdenumcarbide and 10% additional metal. when the additional metal is cobaltthe hardness varies between 65 i and 69 Rockwell for the compositionrange given. By way of comparison it may be stated that the Rockwellhardness of an alloy containing 90% tungsten-monocarbide and 10% cobaltis 60,

- whilst that of an alloy of 90% molybdenum carbide and 10% cobalt is51.

Let me take now the rules given by the science based on theinvestigations of Kurnakow and Zemczuzny in the Zeitschrift fih'anorganische Chemie 1908, volume 60, page 1, and 1910, vol- 5 ume 68,-page 1365, referred to in the standard book of Reinglass "ChemischeTechnologie der Legienmgen, second edition, page 52, 53, and in theMetall-und de of Dr. M. v. Schwarz, Professor of the College at Munich.second edition (1929) page 49. There is referred to the investigationsof Kurnakow and verbatim said: In an uninterrupted series of mixedcrystals the curve of hardness increases with the concentrationgradually up to a flat maxia mum, which lies mostly at the simple atomiccomposition. If Schwam says atomic composition, it is to be consideredthat, he mentions metals and not chemical combinations as carbides. Ifsuch combinations are to be .used, then instead a atoms, existing onlyof the pure metals, the "molecules" are to be taken, because they are incompounds equivalent to the atoms of the single pure metal. Furthermore,science says that the maximum .5; does not always lie at simplemolecular proportions. If one carbide materially exceeds another carbidein hardness, then the maximum of har d ness is "shifted in favor oftheharder carbide in the mixed crystal and consequently two (or three)molecules of the harder (or exceedingly harder) carbide iorm togetherwith one molecule of the softer carbide the mixed crystal of greatesthardness. In other words, the carbides are to be present approximatelyin integer number ratios of their molecular weights, the higher ratioapplying to the relatively harder carbide, in one of the composedcarbides is harder than the other-Q Lastly, if a curve of hardness ofmixed crystals is built up depending on the contentof the respectivecarbides, then the maximum of the curve is hat and does not form a tipso that mixed crystals of about greatest hardness are practically alsoobtained if deviating by about to to both sides from the theoreticalmolecular proportion corresponding to greatest hardness.

Let me take an alloy having 10% auxiliary metal and therefore 90%carbide. Let me further take that tungsten-carbide and titanium carbideare to be mixed to form the hardest mixture. Then we have to dividethese 90% in the proportion of 60:196. this means that we have to takeabout (weight) titanium-carbide, about 70% trmgsten-carbide and about u10% auxiliary metal.

Let me take molybdmum-carbide and titanium-carbide. Titanium-carbide isexceedingly hard, at least harder than molybdenum-carbide, and isfurthermore very light.' Consequently the optimum of-hardness is to beexpected at a proportion of 1:3 (or 1:4). At 1:3 we have about 49.5(that means less than 50%) molybdenumcarbide and 40.5% titanium-carbide,if 10% auxiliarymetal is'present. Consequently I have shown in mycopending. application Ser. No.

- carbide (VC) 575,482 that an alloy containing less than 50%molybdenum-carbide is most advantageous, if the balance is chosen fromtitanium-carbide and auxiliary metal.

. Let me take the carbide of vanadium of the 5 fifth group oi! theperiodical system, and the carbide of tungsten of the sixth group of theperiodical system. Then the correct molecular proportion will be 1:2because tungsten-carbide exceeds in hardness. Consequently the alloywill 10 contain 10% auxiliary metal, about 70% tungsten-carbide andabout.14% vanadium-carbide, corresponding to the molecular weight of 196of tungsten-carbide (WC) and 63 of vanadium- Let me takevanadium-carbide (carbide of the ilfth group) and titanium-carbide(carbide oi the fourth group). Considering that titaniumcarbide exceedsin hardness vanadium-carbide. the molecular proportion is to be chosenwith 20 1:2 and consequently the hard-metal will contain 10% auxiliarymetal, about 60% titanium carbide and about vanadium carbide in order toremain within the range of hardest mixed crystals formed by thesecarbides. Let me take, as last example, boron carbide (of the thirdgroup) and titanium carbide (of the fourth group). Boron carbide isknown as the hardest carbide and consequently a little harder thantitanium carbide. The boroii' car- 31 bids is investigated as 390 with amolecular weight ,of 78. Taking that the hardness or carbides is aboutthe same, the mixed crybfil has to be made of equal p oportions of .themolecules; this means in the proportion 78:60.

. Consequently, an alloy will contain 10% auxiliary metal, about boroncarbide and about 40% titanium carbide. f

I showed by the examples given that either one molecule of each carbideis tobetaken, or two 40 molecules of one carbide and only one moleculeof the other, or three molecules of'one carbide and again one of theother. I must teach the possibility that also two molecules of onecarbideand three of the othercarbides are to be taken a. to form thehardest mixed crystal. There also exist in exceptional cases theintermediate proportion of 3:2.

In the examples given 10% auxiliary metilis chosen only for the sake ofuniformity. ,But the 0 amount of auxiliary metal a. g. of the iron groupand chromium can vary between about 3% and 22%. The amount may besmaller if heavy mixtures of carbides (e. g. tungsten-, molybdenumcarbide) are concerned and larger if lighter mixtures ofcarbides (e. g.with titanium carbide) I are concerned.

As a consequence of the considerations presentcd, the followingcompositions meet niy invention regarding the use of the approximatelyso hardest mixed crystal: 10% to 20% vanadium carbide, 85% to tungstencarbide, 5% to 20% auxiliary metal; 50% to titaniumcarbide, 45% to 25%vanadium carbide, 5% to'25% auxiliary metal; to 40% titanium carbide, 5555% to 35% boron carbide, 5% to 25% auxiliary metal; 10% to 25% titaniumcarbide, 75% to 55% tungsten carbide, 5% to 30% auxiliary metal; 35% to60% tantalum carbide, 35% to 60% tungsten carbide, 5% to 20% auxiliary.metal; 79 70% to 90% tantalum carbide, 5% to.25% vanadium carbide, 5% to20% auxiliary metal; 65% to tantalum carbide, 10% to 30%.niobiumcarbide, 5% to 20% auxiliary metal; 25% to 7 hardness accordingto the theory and nickel up auxiliary metal.

to 9% and 15% and chromium up to 1% and 2% as auxiliary metals has beenproved.

Whatever be the procedure in the formation,

suitable admixture, and containing sometimes a few per cent (1% to 10%)of carbide as forming one or more (or all) constituents of the mixedcrystals.

As I stated already in my copending application Serial Number 352,132,also ferrovanadium may be used as auxiliary metal. Ferrovanadiumcontains about 20% iron and melts like iron or cobalt between about 1450to 1500 C. I sug gested in the above mentioncdapplication to add such anauxiliary metal, like ferrovanadium, in amounts up to about 10%.Consequently such a hard metal according to my copending applicationcomprises up to about 10% auxiliary metal melting between about 1450"and 1500 C., and about carbide. If choosing the range of hardest mixedcrystals formed e. g. by WC and MOzC, as mentioned in my applicationreferred to hereinbefore, then immediately according to the generalscience existing prior to my invention as presented liereinbefore, theproportion of the carbide contained can be calculated, namely WC about60% and Mo'zC about 30%, and the range of such carbidesatisfying thescience to form hardest mixed crystals lies between 54% and 66% WC, 27%and 33% M020, balance auxiliary metal like ferrovanadium (on an average10%).

The carbides produced are, if needed, powdered again and intimatelymixed with carbide, if desired, and the chosen auxiliary metal ormetals. mentioned before. The mixtures are then preformed by pressing insuitable moulds to a shape similar to the desired shape. There is to betaken into calculation the shrinking which takes place 'during thefollowing treatment.

An electric furnace can be employed for effeeling the heating andsintering; the sintering may also be carried out by means of highfrequency currents. good results are obtained by carrying out theheating or sintering. in a vacuum.

If mixed crystals of more than two carbides are to be contained in thecomposition. one proceeds with advantage in such a way that first atleast two groups of binary crystals in solid solu tion are formed, eachgroup comprising different carbides, whereupon these groups are combinedinto tenary or quaternary mixed crystals in solid solution and thencompacted with auxiliary metal. Those groups of mixed crystals, and themixed crystals combined of the groups, are preferably formed beforeaddition of substantial amounts of The latter may be added, however, insubstantial or even in their entire amount Suitable proportions havealready been In some cases particularly to the groups of mixed crystalsbefore final compacting or sintering.

Auxiliary metal may be added in trifling amounts to the originalcarbides when forming the binary mixed crystals, and either smallamounts or the entire amount of the auxiliary metal may be added whenforming the quaternary mixed crystals, the latter fo'rmation occuringsimultaneously with final sintering of the composition.

There exist several ways of explaining the surprising result of theinvention, although the inventcr declines to limit the invention or tohas iton any theory.

According to the theory applying to mixed crystals, the mixed crystal isharder than the components. If, therefore, two mixed crystals are causedto permeate each other to form a new ternary or quaternary mixedcrystal, it can readily be expected that the mixed crystal so formed isharder than the components. This means that the combined mixed crystalsare harder than the parent mixed crystals and because of the fact thatthe latter ones are harder than the single carbides from vwhich they areobtained, the final mixed crystal has to be harder also than thecarbides themselves. I

It is satisfactory for the invention if only substantial amounts of suchmixed crystals are present. According to experience already about 10% ofthe ha d metal alloy formed by mixed crystals are capable ofconsiderably improving the properties of the hard metal. If about halfof the present carbides or more are transformed into mixed crystals, adecisive improvement can be ascertained. Besides, auxiliary metal may be1 present in amounts of from about 3% to 25%.

The amounts of mixed crystals of carbide of elements taken from thethird, fourth, fifth, and/or sixth group of the periodical system mayconveniently amount to at least from about 35% to 45% of the alloy, upto about 75% to of it, and auxiliary metal preferably taken from theeighth group of the periodical system, and especially from the irongroup, in amounts from. about 5% to about 25% by weight of the alloy.

It is quite difficult to mention any minimum amounts of carbide to bepresent, because 5% titanium-carbide occupy .a space four times as largeas 5% by weight of tungsten-carbide. Nevertheless, the minimum amount ofcarbide to be present and forming part of a mixed crystal according tothe invention, has to be substantial and, as a minimum, about 1% byweight of the alloy.

The preforming or shaping of the initial mixture. containing two or morehard carbides and auxiliary metal according to the invention in finelydivided, or as finely divided a form as possible, in the moulds may bedone also under elevated pressure, up to several atmospheres per squarecentimeter, say up to 50 to 75 atmospheres and higher.

The body so preformed and advantageously still under pressure is now tobe sintered. It is done by electrical current led through the bodyitself or around the body through the mould.

Any other kind of heating is applicable.

The temperature of the body is to be elevated to about 1400" to 1600 C.and this heat-treatment is to be continued for about one or severalhours, or parts of them,till the wanted structure of the body isachieved. v 1

Generally, the body according to my invention is consolidated-by usingauxiliary metals of the kind and in the amounts as mentioned before andsintering it at elevated temperature, say in the range up to about 1400C. to 1600 C.

In case, however,- difiicult forms of the body are to be produced notachievable by usual moulds, or in case sharp edges are desired, orangles diflicultly' to manufacture in such a way, so that the mechanicalworking or finishing of the hard metal body is needed after sintering,then the following ways are preferable.

The pressed and preformed body is to be submitted to sinteringtemperatures as mentioned before, but such sintering should be doneduring a short period of time only, say for 1 to 5 to 10 minutes so thatthe particles are sufficiently fritted together to withstand mechanicaltreatment without presenting, however, the hardness of a fully sinteredbody. Such a body is then subjected to finishing in any way and then thesintering at the same temperature is continued until the fully sinteredbody is achieved.

Surprising results have been further achieved by adding oxide of metalsor metalloids not being reducible by hydrogen and not, or only at hightemperatures, forming carbides. Such oxides are presented by alumina,silica, the earth alcalis, the

group comprising zirconium and the group comprising the rare earthmetals. Especially the addition of alumina in the finest divided form inrelatively small amounts, say up to about 0.5% has caused the formationof most suitable alloys of the herein mentioned various compositions.

When I refer in the appended claims to carbide of elements selected fromthe third, fourth, fifth and sixth group of the periodical system, Imean carbides adapted for use in hard tool elements, having a suitablehardness and not being dissolved by water or other liquid employed forcooling or similar purposes at operation temperatures. Such carbides areboron-carbide (belonging to the third, group), titanium-carbide,

silicon-carbide, zirconium-carbide (belonging to the fourth group),vanadium-carbide, niobiumcarbide, tantalum-carbide (belonging to thefifth group), and tungsten-carbide, molybdenumcarbide andchromium-carbide (belonging to the sixth group).

For the sake of clarity, I expressly state that the consolidation of thebody can be done in the presence of auxiliary metals being heated andalloyed, as a whole, with the carbides present, or alloying only, moreor less superficially with one or all carbides present, or not alloyingat all'with them as the case may be due to the relative properties ofthe auxiliary metals and carbides present.

Tool alloys prepared according to the invention are, as a rule, not usedfor the production of the entire tool, but merely for the part of thetool which in practice is used directly for cutting, drilling, etc. andwhich is subject to wear.

From the above description it appears that the carbides to be cementedby auxiliary metal may be transformed into mixed crystals entirely or insubstantial amounts before substantial amounts of auxiliary metal areadded. The mixed crystals are formed by heat treatment. Growth ofcrystals (re-crystallization) is either prevented by'.the presence ofauxiliary metal or can be prevented through addition of traces ofalumina, silica, ,etc., as explained hereinbefore. It has also beenfound that mixed crystals resist re-crystallization to a large extent.Thereby finest grain of carbides present in the alloy including'mixedcrystals is retained, and a tough and very eflicient, clean cuttingmaterial is obtained.

If carbides highly resistant to oxidation are combined with mixedcrystals and other carbides less resistant to oxidation, the'resistivityof those mixed crystals against oxidation sur-' passes that of thecarbide of originally lower resistivity. However it has 'been found,that the mere presence of carbide of higher resistance to oxidation infinely divided form close to carbides loy, in particular for tools andparts thereof, the 1 steps of mixing auxiliary metal substantially of.the iron group in amounts from about 3% to 22% and at least two hardand refractory carbides in substantial amounts of elements selected fromthe third, fourth, fifth and sixth group of the periodical system, saidcarbides present in finely divided state and insuitable proportions toyield approximately hardest mixed crystals when alloyed, suchapproximate proportions indicated by integer number ratios between andincluding 1:1 to about 1:3 of the molecular weights of the containedcarbides, shaping the mixture and alloying said carbides and metal bysintering at temperatures between about 1400" C. to 1600 C. until saidmixed crystals are formed in substantial amount.

2. In a method of producing a hard metal alloy, in particular for toolsand parts thereof, the steps of mixing auxiliary metal substantially ofthe iron group in amounts from about 3% to 22% and at least two hard andrefractory carbides in substantial amounts of elements selected from thethird, fourth, fifth and sixth group of the periodical system, saidcarbides present in finely divided state and in suitable proportions toyield approximately hardest mixed crystals when alloyed, suchapproximate proportions indicated by integer number ratios between andincluding 1:1 to about 1:3 of the molecular weights of the containedcarbides, shaping and pressing the mixture and alloying said carbidesand metal by sintering at temperatures between about 1400C. and 1600 C.until said mixed crystals are formed in substantial amount.

3. In a method of producing a hard metal alloy, in particular for toolelements and other working appliances, the steps of comminuting asfinely as possible at least two hard carbides of differentelementsselected from the third through sixth group of the periodical system,admixing the selected carbides in substantial amounts, including aminimum of 1% of a selected carbide, with auxiliary metal substantiallyof the iron group in amounts of about 3% to 22%, shaping said mixtureand finally alloying it by sintering into a hard and tough body and,until mixed crystals of said selected carbides are and sixth group ofthe periodical system, ad-

mixing said selected carbides in substantial amounts, including aminimum of 1%, of a selected carbide, with auxiliary metal essentiallyof the iron group in amounts of about 3% to 22%, shaping said mixtureand finally alloying it by sintering into a hard and tough body anduntil mixed crystals of said selected carbides are formed in substantialamount, including a minimum of about 10%, the hardness of which exceedsthat of any carbide contained in said mixed crystals. I

5. In a method of producing a hard metal alloy, in particular for toolelements and other working appliances, the steps of comminuting asfinely as possible at least two hard carbides of elements selected fromthe third, fourth, fifth and sixth group of the periodical system,admixing said selected carbides in substantial amounts, including aminimum of -1% of a selected carbide, with auxiliary metal essentiallyof the iron group in amounts of about 3% to 22%, shaping and pressingsaid mixture and finally alloying it by sintering into a hard and toughbody and until substantial amount,'ineluding a minimum of about 10%, of.said selected carbides form mixed crystals, the hardness of whichexceeds that of any carbide contained therein.

6. In a method of producing a hard metal allay, in particular for toolelements and working appliances, the steps of comminuting as finely aspossible at least two hard carbides of elements selected from: the thirdthrough sixth group of the periodical system, admixing said selectedcarbides in substantial amounts, including a minimum of 1% of a selectedcarbide, and in proportions suitable to yield approximately hardestmixed crystals, with auxiliary metal essentially of the iron group inamounts of about 3% to 22%, shaping said mixture and finally alloying itby sintering into a hard and tough body and until said mixed crystalsare formed in substantial amount, including a minimum of about 10%.

"I. In a method of producing a hard metal composition, in particular'for tool elements and other working app1iances,- the steps of finelycomininuting at least two hard carbides of different elements selectedfrom the third through sixth group of the periodical system, admixingthe selected carbides in substantial amounts, including a minimum of 1%of a selected carbide, with auxiliary metal substantially of the irongroup in amounts of about 3% to22%, shaping and pressing said mixtureand finally alloying' it by sintering into a hard and solid body anduntil mixed crystals of said selected carbides are formed therein insubstantial amount, including a minimum of about 10%.

PAUL SCHWARZKOPF.

